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Abstract: The authors propose a specific methodology and definitions to determine the energetic efficiency of any energy production system and process therein, in agreement with the laws of physics and taking into account technical constraints. The method rests on the calculation of a modular indicator, the expenditure rate, ratio of the energetic costs to the gains of the system. An expenditure rate above 1 questions the system efficiency. We underline the importance of the data sources and of their uncertainties to calculate the expenditure rate starting from the deconvolution of a system in various stages, from the extraction of the natural resource to its final form of use, including the materials, the losses, and the energy contributions. As the efficiency indicator does not inform us about the extractible amount of the studied resource and of others, it should be completed with a specific study about their reserve and future production (where the expenditure rate acts as a criterion). [Copyright &y& Elsevier]

Abstract: Nitrogen fixation, nitrate assimilation and primary production (13C/15N method) were investigated during one year and half in the northwestern Mediterranean Sea. Nitrogen fixation was detectable all over the year with rates ranged from 2 to 17 nmol N l−1 d−1 d. Highest values being obtained during spring associated with the phytoplankton bloom. High rates (4–8 nmol N l−1 d−1 d) were also measured during summer, when primary productivity was very low. Then, diazotrophy process supplies significant new nitrogen during summer oligotrophic periods. This new nitrogen input can balance the annual nitrogen biogeochemical budget in the Mediterranean Sea and should explain the high nitrate/phosphate ratio observed in deep waters. To cite this article: N. Garcia et al., C. R. Biologies 329 (2006). [Copyright &y& Elsevier]